1. Field of the Invention
The invention relates to an apparatus for remotely repairing the tubes and tubesheet of a steam generator, and more particularly to such an apparatus that can be remotely installed in and removed from a steam generator and which provides for quick change of ancillary devices such as tools.
2. Description of the Prior Art
In a variety of environments it may be highly desirable to provide a platform or carriage from which various types of work can be conducted remotely. Furthermore, it may be necessary to move the work station relative to the surface or member on which the work is being conducted. Space limitations or biological considerations may make it desirable to control such movement remotely. A prime example of this need is presented by a nuclear steam generator, where it may be necessary to inspect or repair some of the tubes inside the steam generator. Normally, these repairs are only required after the steam generator has been operated, which naturally renders the steam generator radioactive. The level of radioactivity within the steam generator may seriously limit the amount of time a man can spend in the environment. In addition, to work in this environment at all a man must wear bulky and heavy protective gear which severely restricts his mobility, vision and stamina. Therefore, it is desirable and sometimes perhaps necessary to provide remotely operable and controllable means for performing the required work.
Numerous prior art devices for performing specialized functions, for example directing an eddy current probe through the tubes, have been developed. One such effort is disclosed in U.S. Pat. No. 3,913,752, issued to Ward et al. on Oct. 21, 1975, which is commonly referred to as a "finger walker" within the industry. Such devices are slow, cumbersome, difficult to control and locate precisely and do not retain a firm hold on the tubesheet. Therefore, they are not capable of carrying heavy loads. In addition, such a manipulator is not capable of operating in the top head of a once through steam generator. Furthermore, such devices must be installed and removed by a person who is inside the hazardous steam generator.
Another such device is disclosed in U.S. Pat. No. 4,216,832 issued Aug. 12, 1982, to Galtthorne. This device also is capable of operating only in the bottom head of a recirculating steam generator. Furthermore, this device and others of its kind are not capable of remote installation in and removal from a nuclear steam generator. A man must go inside the head of the steam generator to install the device and to remove it.
Although the time required for installation and removal of the device is less than would be required for a man to enter the steam generator and actually perform the required work, many of the disadvantages of having a man work inside the steam generator still arise because he must be available to install and later remove the device, with the consequent exposure to radiation this entails. Radiation levels inside a nuclear steam generator are two to three times higher than those outside it, even when emissions from the manway are included in outside radiation measurement. Thus a remotely installed and removed apparatus would substantially reduce radiation burn out of jumpers, lowering labor costs and reducing personnel needs.
One effort to overcome this difficulty is disclosed in general terms in European patent application publication No. 0 066 791 published on Dec. 15, 1982 invented by Vermaat. In Vermaat, the top of the supporting pole is detachably connected to a mounting rod which extends outside the access port of the steam generator, commonly referred to as a manway, and is held by a man who guides an anchor pin into the tubesheet. The main arm is then guided through the manway on a channel rail and attached to the bottom of the supporting pole. From this position, the main arm is moved up the supporting pole to the work position. In a second embodiment, the apparatus is previously assembled with the main arm being already attached to the supporting pole. In this case, it is not necessary that the main arm be run into the steam generator on the channel rail. Still, however, a man must lift the apparatus to the top of the head of the steam generator, locate the locator tubes and install the anchor pins in the appropriate tubes. The tubes of a nuclear steam generator are typically 5/8" in diameter and are closely packed. It is essential that the anchor pins be located in the correct tubes; otherwise the device will not know where its tool is located. The apparatus weighs in excess of 100 pounds and must be raised approximately five feet by a man who is laterally removed from the apparatus by three or four feet. In addition, the man must wear protective clothing to shield him from the radiation emanating from the manway. Thus, installation of this apparatus in either embodiment is a skilled operation requiring great strength combined with considerable dexterity. In addition, the apparatus is capable of operation only in the head of a recirculating steam generator.
Therefore, a need exists for an apparatus which can be remotely installed and removed from a steam generator, which can be operated in a recirculating steam generator, or in the top or bottom head of a once through steam generator, which is capable of reaching nearly all the tubes of a recirculating steam generator or a once through steam generator from one location, and which can reach all tubes of a once through steam generator with one change of position and which is capable of performing a variety of operations with a variety of tools that can be quickly changed while maintaining the ability to locate any individual tube with any individual tool and which accordingly is capable of sustaining high loads and forces without substantial deflection.